Safety paper



Patented July 23, 1940 PATENT OFFICE SAFETY PAPER William Whitehead, Cumberland, Md., assignor to Celanese Corporation oi. America, a corporation of Delaware No Drawing. Application January 28, 1937, Serial No. 122,789

2 Claims.

This invention relates to identifiable paper or other cellulosic materials, and to the process for making the same, wherein the mark of identification is in fiber form, which fibers are soluble in solvents that have no effect on the cellulosic fibers and which fibers may be colored in a manner so that they are completely fast to acids, alkalies, etc. and which can be made fast to bleaching agents.

.An object of the invention is the economic and expeditious production of cellulosic materials,

' such as paper, cardboard, felts, etc., which have incorporated therein fibers, made of or containing an organic derivative of cellulose, as a mark. of identification or as a decoration. A further object of this invention is the production of paper to be used as money, stock certificates, revenue stamps and the like, the authenticity of which paper may be determined by simple tests since the paper contains fibers which may be dissolved out by means of solvents which have no efiect upon the paper andsince the fibers may have one ,or a plurality of definite diameters. Another object of the invention is the method of incorporating fibers made of or containing organic'derivatives of cellulose in paper, cardboard or other cellulosic materials. Other objects of the invention will appear from the following detailed description.

Paper heretofore has been manufactured having incorporated therein short lengths of silk fibers as a means of identification. Thispaper has been used mostly in currency. The silk fibers are of twofold importance, firstly, for the reason that they show the paper to be of a certain type and, secondly, because colored fibers in the paper make more difficult the photographic reproduction of the printed matter on the paper. I have found that by incorporating fibers made of or containing an organic derivative of cellulose in paper many advantages are sition, and the fibers may be present in various proportions such that upon a microscopic examination of the paper the authenticity of the same is easily ascertained. Another advantageof the present invention is that the threads may be dissolved from the paper without-affecting the paper, thus giving rise to a very simple test for the authenticity of the paper. Further-- more, by employing this invention, identification marks may be made resistant to or unaffected by bleaching agents or the paper may have some identification marks which cannot be removed by a bleaching operation and others which can 5 be removed by a bleaching operation.

In accordance with my invention, I form sheet cellulosic material, such as tissue paper, writing paper, cardboard or other types of material from any suitable cellulosic materialland incorporate in said cellulosic material fibers formed of or containing an organic derivative of cellulose of any desired denier, color, length or mixtures of such organic derivative of cellulose fibers. The fibers made from or containing an organic derivative of cellulose may be incorporated in the cellulosic material in any suitable manner. However, in accordance with this invention, I prefer to incorporate the organic derivative of cellulose fibers in the paper stock or pulp either before the heater or before or after the Jordan by feeding to the stock a uniform amount of the fibers. This may be accomplished by feeding a lap or roving formed of an organic derivative, of cellulose fiber to the paper stock or by forming a suspension of the said-fiber and flowing it into the paper stock.

The base material of the paper or other cellulosic material may be any suitable stock normally employed in the formation of such cellulosic materials. For instance, the paper or other cellulosic material may be made from wood or vegetable pulps made by the mechanical method, -soda method, sulphate method, sulphite method or combinations of these, or. from cotton and linen rags or masticated paper or mixtures of these. The paper or other cellulosic material may be formed on the same machines and in the same manner as previously. For instance, this invention is applicable to hand methods of making paper, cardboard and the like or to the machine methods wherein the pulp is mixed, then passed through a, beater, a Jordan, blending tanks and onto a sluiceway to-the screens or Fourdrinier. The paper vor cellulosic material materials that are to be used for any purpose where ready identification is an objective. For instance, this invention may be employed to produce papers of suitable thickness and weight adaptedto be used as currency, revenue stamps,

stock certificates and bonds, official seals, closure seals for bottles, boxes or other containers.

This invention is also of importance in the manufacture of cardboard for boxes or closure members of containers, pass cards and the like. In the above applications of the invention the problem of ready identification and the difliculty of duplication is of major importance. The invention, however, has also another object, i. e. that of decoration. In the above applications of the invention the decorative feature may be incorporated along with the protective feature, or the invention may be used purely for decorative efiects in, for example, tissue paper, either of the soft or glazed variety, used as wrappings for bottles, articles, packages and the like. Here also the protective feature may be of some importance in that each manufacturer may have a particular color, denier or mixtures of colors and deniers which make the origin on the wrappings [of the packages easily determined. This in- -'vention may be used to produce wall paper, coverings for individual packages or boxes and the like. For instance, paper may be made, such as wall paper, or coverings for cardboard boxes, employing a mixture of organic derivative. of cellulose fibers and printing or dyeing the organic derivative of cellulose fiber after it is in the paper. For instance, a wall paper may include organic derivative of cellulose fibers of difierent .color, denier and pigmentation, as well as an organic derivative ofcellulose fiber of natural color. A printed design may be imposed on the paper by employing dyes having an amnity for cellulosefiber and no aifinity for an organic derivative of cellulose fiber and/or dyes having an affinity for the organic derivative of cellulose fiber only and not for cellulosic materials. Multiple color effects in papers are thus produced through the difierential dyeing or printing imposed thereon and through the pigment or coloring matter already in the organic derivative of cellulose fibers. Such paper would be impossible. to duplicate without starting with the io'rmation of the paper and then only when the percentages of the various components are known.

Any suitable type of organic derivative of cellulose fiber may be employed in making identification marks in or on the cellulosic material. For ,instance, fibers formed of the organic esters of cellulose and cellulose ethers may be employed. Examples of the organic esters of cellulose are cellulose acetate, cellulose iormate, cellulose propionate and cellulose butyrate, while examples of cellulose ethers are ethyl cellulose, methyl cellulose and benzyl cellulose.

The organic derivative of cellulose fibers may be formed by spinning into the form of substantially continuous filaments a solution of an organic derivative of cellulose dissolved in a suit-' ;lidifyii'igmedium, such as a drying atmosphere according to the drymethod of spinning, or into a a precipitating bath as in the wet method {of' spinning. The substantially continuous filaments as individual filaments, bands, bundles -ductlon of identifiable paper or other cellulosic or hanks may then be cut or torn into suitable lengths. The fibers'incorporated in the cellulosic article may be of any suitable length, for

instance, from 5 of an inch to 3 or more inches.

The organic derivative of cellulose fiber may be relatively straight or the same may be embossed, or treated in liquids, to impart to the fiber a curl, crimp or other configuration. If desired, the fibers, or the filaments before being cut or torn into fibers, may be intermittently embossed by such means as heated embossing rolls to form segments which have a definite configuration, while other segments have their natural fiber-like shape.

The organic derivative of cellulose fibers may contain besides the organic derivative of cellulose base material, efiect materials such as pigments,

' plasticizers, dyes, lakes, filling materials, fire retardants and the like. These materials may be incorporated in the fibers by adding the effect materials to the solution of organic derivative of cellulose prior to its formation into filaments, or the same may be added tothe formed filaments or fibers in any suitable manner. For instance, the fibers may be dyed by means of dye baths with or without the aid of swelling agents and the like. Pigmented fibers are of exceptional value as fibers of identification. The pigmented fibers may be of any suitable color from white to' black. They may be formed by mixing with the spinning solution from which the fibers are formed such pigments as the metal oxides, carbonates, phosphates, etc. For instance, a white fiber may be formed by incorporating titanium, zinc or lead oxide in a fiber, while red fibers may be produced by incorporating iron oxide or the like in a fiber, and blue fibers may be formed by incorporating Prussian blue therein. Besides the metal oxides, hydroxides. or other metal salts, there may be employed as pigments insoluble or relatively insoluble organic com-' pounds.

The fibers of an organic derivative of cellulose employed in the making of the cellulosic materials may be of any suitable denier or mixtures of denier. For instance, fibers having a denier of 0.3 up to 20 or more may be employed or mixtures of any desired deniers may be employed. In the manufacture of the organic derivative oi cellulose fiber by means known in the art, the fibers may be made to have a denier which varies in any desired ainount over a given length. When these fibers are cut into the length desired in the finished paper the fibers show this varying denier which gives rise to a stillfurther means of determining the origin of a paper; In stamps, stock certificates, currency and the like it is often desirable to incorporate in the cellulosic base material a low denier fiber, say 0.5, as a means of making diflicult the photographic reproduction of the article, and then large denier fibers, say 3 to 10 denier, ior a ready or more visible determination of the authenticity of the article. Obviously, the fibers of the same denier or of each denier may be of the same or of a difierent color.

The'fibers' of an organic derivative of cellulose may be dyedrany suitable color prior to incorporation in the cellulosic material or the fibers may be of natural color. I have found that organic derivative of cellulose fiber containing a and the like, although the fiber may readily be formed of an organic derivative of cellulose or not, whereas placing the cellulosic material in a bleaching agent is a ready test as to whether the fibers are pigmented or dyed. The organic derivative of cellulose fibers may be partially saponified or intermittently saponified, whether they be pigmented or not, to change their afllnity for printing inks,- dyes, etc. The use of the intermittently saponified fibers gives rise to still another possibility of identifying the origin of the certain cellulosic material since the saponified segment of the fiber of identification is dissolved in different solvents from the other segment.

Thus, in accordance with my invention, the origin of cellulosic material is ascertained by easy and simple tests such as the size of the identification fibers, the number of different sizes or whether the fibers are bleach-proof or easily bleached. For instance, different types of fibers may be placed in a paper, such as large denier fibers, small denier fibers having a curl or crimp to interfere with photographic reproductions or, say, a black fiber unaffected by bleaching, mixed with a red fiber easily bleached or any other combination of the fibers described above.

The organic derivative of cellulose fiber may be incorporated in the paper in any suitable manner. However, I have found it of advantage to form the organic derivative cellulose fiber into a sliver of fairly uniform weight. By this means, where more than one type of organic derivative of cellulose fiber is employed, the proper distribution or mixing of the product is easily obtained.

This sliver whether in spool form or canned is drawn to the stream of paper stock either before it enters the Jordan or after it has passed through the Jordan prior to reaching the screens and there it is broken down into the individiial filaments by means of water jets, heaters, air or other means and mixed into the paper stock.

In place of forming the fibers into a roving, I

may form the fibers of organic derivative of cellulose into a lap by meansof a cotton or wool carding device. This lap is pulled between nip rolls to a point above a flowing stream of paper stock and by means of heaters, air jets or other means broken down to the individual fibers, and the fibers forced into the stream of paper stock passing therebeneath. If it is desired to place the marks of identification only on predetermined sections of the paper this may be done by feeding the organic derivative of cellulose fiber to the paper stock where the paper stock meets the screens. Here the organic derivative of cellulose fibers may be fed to the paper stock in rows, bunches or otherwise.

I have also found that the organic derivative of cellulose fibermay be mixed with the paper stock by forming'a slop of the organic derivative of cellulose fiber in water by the addition of from 1 to 5% on the weight of organic derivative of cellulose fiberof tapioca, starch, dextrin and the like. Tapioca, starch, dextrin and the like gives to the mixture of water and organic derivative ev nly dispersed or suspended in the liquid in such a manner that the mixture may be poured over the edge of a into the stream of water pulp. If tapioca, starch, dextrin or the like is in the mixture to drain from the organic derivative of cellulose fibers which are left in the tank. Tapioca, starch and dextrin also act as a protective colloid for the fibers.

Any suitable percentage of organic derivative of cellulose fibers may be mixed with the cellulosic fiber stock. A suitable amount for stock certificates, bonds and revenue stamps, when employing a dark colored fiber, is a 5 denier organic derivative of cellulose fiber in an amount equal to about 1 to 4% based on the weight of the fiber. Obviously, smaller or greater percentages of each may be employed according to the result desired. I In the manufacture of wall paper, coverings for cardboard or the cardboard boxes themselves as high as 20 to 30% of organic derivative of cellulose fiber, based on the weight of the product, may be employed.

As an illustration of this invention, but without being limited thereto, the following examples are given:

' Example I By means of a cotton card a lap is formed from 5 denier cellulose acetate fibers containing a carbon black pigment. A slurry of a sulphite wood pulp containing about 10% of linen or rag pulp is formed in the usual manner. To the stream of sulphite pulp flowing from the Jordan onto the screen is added the cellulose acetate fibers in an amount equal to 3% on the weight of the air dried paper. The addition of cellulose acetate fiber to the stream of sulphite pulp is accomplished by drawing the lap through nip rollers at a constant speed to give the desired percentage of fibers and beating with mechanical beaters the end of the lap as it comes through the nip rollers in a manner to knock the fibers free from each other and into the stream of sulphite pulp. The paper is found to havethe cellulose acetate fibers evenly dispersed therein, The cellulose acetate fibers are readily visible, and may be dissolved from the paper by dipping the paper in acetone. The color of the cellulose acetate fibers is unchanged upon treating the paper with bleaching agents.

Example II carried through the Jordan, filters and onto the screen. The paper is found to have the cellulose acetate fibers evenly distributed therein. The cellulose fibers are of substantially the same length as when placed in the mixture and they are readily identifiable by the tests set forth above.

It is to be understood that the foregoing detration and that many variations may be made therein without departing from the spirit of my invention.

5 Having described my invention, what I desire to secure by Letters Patent is:

1.- Safet'y'paper comprising a body of cellulose tailed description is given merely by way of illusfibers having fibers containing cellulose acetate embedded therein in separated relation and at least some of which cellulose acetate fibers are visible in said body, said cellulose acetate fibers being of at least two different deniers and of at least two different colors and in a quantity from 1 to 4%, based on the weight of the product, whereby they can be removed from the material without impairing the properties or quality of the remaining part of theumaterial.

WILLIAM WHITEHEAD. 

